Device for connecting a longitudinal bar to a pedicle screw

ABSTRACT

The invention relates to a device for connecting a longitudinal bar to a pedicle screw thereby forming a system for fixation of the spine. The device includes a body having an upper end, a lower end, a hole which is open at least towards the bottom and has an axis, and a through hole positioned perpendicular to the axis. The device also has a collet chuck mounted coaxially on the inside of the body in such a way that it can slide along the axis. The collet chuck has a through hole which is flush with the through hole of the body, and a chamber which faces at least downwards and is defined by tongues spring-mounted against the cylinder axis. When the collect chuck is inserted in the body, the through holes align to allow insertion of the longitudinal bar. The head of a pedicle screw can be clicked into the chamber from below by spring-action. The device is easy to use and makes it possible for the pedicle screw to be inclined within a certain range.

[0001] This invention will provide a remedy in this regard. Thisinvention is based on the problem of creating a device for connecting alongitudinal bar to a pedicle screw, said device being easy to handleand permitting bending of the pedicle screw within a certain range.

[0002] This invention achieves this object with a device having thefeatures of claim 1.

[0003] In one embodiment, the desired number of devices according tothis invention can be aligned on a longitudinal bar and can be simplysnapped onto the pedicle screw with a spherical head already implantedin the vertebrae, so that a primary connection between the longitudinalbar and the pedicle screw is established. Other embodiments of thedevice according to this invention permit subsequent insertion of thelongitudinal bar from the side or from above. By screwing the set screwinto the fixation device, the longitudinal bar is locked axially andrelatively in the device at the same time, and the device is secured ina stable angular position. The set screw presses on the longitudinal barinserted into the device, and the longitudinal bar presses on thebushing of the fixation device, and the bushing braces the collet chuckon the preferably spherical head of the pedicle screw by way ofcorresponding, preferably conical inside surfaces of the bushing andoutside surfaces of the collet chuck.

[0004] Other embodiments in turn permit sequential and independentlocking of the longitudinal bar and rotation of the device with respectto the pedicle screw.

[0005] Thus, in comparison with known devices, the device according tothis invention offers the advantage that the pedicle screws can not onlybe secured exactly perpendicular to the longitudinal bar but also permitan angle bend of up to ±25°. This is especially important if thelongitudinal bar has not been bent accurately, which leads to majorproblems in assembly with traditional systems.

[0006] A preferred refinement of the device according to this inventionconsists of the fact that it also includes a pedicle screw with apreferably spherical head. The head of the pedicle screw is preferablyprovided with structuring in the form of transverse grooves ortransverse ribs to achieve better fixation (bracing against the colletchuck). To be able to screw these pedicle screws into the bone, they arepreferably provided with a hexagon socket in the spherical head.

[0007] This invention and refinements on this invention are explained ingreater detail below on the basis of embodiments.

[0008] The figures show:

[0009]FIG. 1: an exploded perspective view of the device according tothis invention together with a longitudinal bar, a pedicle screw with aspherical head and a set screw;

[0010]FIG. 2: a slotted longitudinal section through the deviceaccording to this invention as shown in the plane of the drawing in FIG.1;

[0011]FIG. 3: a perspective view of the device according to FIG. 1 inthe mounted state after locking the longitudinal bar and the pediclescrew by means of the set screw;

[0012]FIG. 4: a perspective view of one variant of the device shown inFIG. 1 with an adjusting nut and a divided bushing;

[0013]FIG. 5: a perspective view of one variant of the device shown inFIG. 4 with a channel on the collet chuck that is open at the top andwith a securing pin;

[0014]FIG. 6: a perspective view of one variant of the device shown inFIG. 1 with an adjusting nut for securing the spherical head of thepedicle screw and a set screw for locking the longitudinal bar;

[0015]FIG. 7: a longitudinal section through one variant of the deviceillustrated in FIG. 6 with a set screw integrated into a locking screw;

[0016]FIG. 8: a perspective view of one variant of the device shown inFIG. 5 with a collet chuck that is open at the side to accommodate thelongitudinal bar and an adjusting nut as a chucking means for lockingthe longitudinal bar while at the same time securing the spherical headof the pedicle screw;

[0017]FIG. 9: a perspective view of the device shown in FIG. 5 without asecuring pin;

[0018]FIG. 10: a perspective view of one variant of the device shown inFIG. 5 with a set screw and an inside thread in the collet chuck;

[0019]FIG. 11: a perspective view of one variant of the device shown inFIG. 8 with an adjusting nut for securing the spherical head of thepedicle screw and with a set screw for locking the longitudinal bar;

[0020]FIG. 12: a perspective view of one variant of the device shown inFIG. 11 with a collet chuck that is open at the top;

[0021]FIG. 13: a perspective view of one variant of the device shown inFIG. 11 with a through hole which is open at the side in the bushing;and

[0022]FIG. 14: a perspective view of one variant of the device shown inFIG. 12 with a through hole which is open at the top in the bushing.

[0023] The device according to this invention illustrated in FIGS. 1 and2 consists essentially of a body 3 in the form of a hollow cylindricalbushing with an axis 4 (axis of the hollow cylinder) and a hollowcylindrical collet chuck 7 arranged coaxially so it can slide in theinterior of the body 3.

[0024] The body 3 has a through hole 6 running across the axis4—intersecting the cylindrical surface of the hollow cylinder at twopoints symmetrically with the axis 4—and the collet chuck 7 has athrough hole 17 running across the axis 4. Insertion of a longitudinalbar 1 running across the axis 4 is made possibly by the alignedarrangement of the through holes 6 and 17 as illustrated in FIG. 2.

[0025] In its upper part, the collet chuck 7 is secured within the(hollow cylindrical) body 3 by a press fit and can be displaced axiallywith respect to the body 3 when the relatively high force of the pressfit is overcome.

[0026] The (hollow cylindrical) body 3 and the collet chuck 7 arepreferably in a rotationally locked arrangement relative to one another,e.g., by means of suitable groove/channel guides running axially. Thecollet chuck 7 is designed with tongues 8 spring mounted against thecylinder axis 4 and pointing downward; the spherical head 9 of a pediclescrew 2 can be snapped from below with a spring action into the chamberformed by these tongues.

[0027] A hole 10 with an inside thread 11 is provided in the upper partof the collet chuck 7 to accommodate a set screw 12 with a hexagonalsocket head 20 which can exert a force on a longitudinal bar 1 insertedinto the device, so the longitudinal bar 1 is locked axially androtationally with respect to the body 3, as indicated in FIG. 3. Thecollet chuck 7 is designed at its lower end such that the screw shaft 13of the pedicle screw 2 connected to the spherical head 9 can be lockedat an angle α of −25° to +25° with respect to the axis 4.

[0028] At its lower end 24, the body 3 has a conical inside surface 14which becomes wider toward the lower end and can come into slidingcontact with a suitably designed conical outside surface 18 of the freeends of the tongues 8 of the collet chuck 7. As soon as the set screw 12abuts against the longitudinal bar 1 inserted into the device, thecollet chuck 7 begins to push upward against the body 3. This process isillustrated in FIG. 2, where the left half of the figure shows thecondition before pushing collet chuck 7 upward, and the right half showsthe conical surfaces 14 and 18 slipping past one another as the colletchuck 7 is pushed upward, with the tongues 8 of the collet chuck 7,which are designed with a spring action due to the slot 22 being pushedtoward cylinder axis 4, so that the hollow spherical cavity 19 isreduced in size, and the head 9 of the pedicle screw 2 inserted into itis gripped securely. To optimize the locking of the head 9, it isprovided with a structuring 15, preferably in the form of transversegrooves or transverse ribs. Otherwise, pedicle screw 2 corresponds tothe known screw designs and is expediently provided with a hexagonalsocket head 16.

[0029] The hollow spherical cavity 19 may in turn be provided with astructuring 21, preferably in the form of transverse grooves ortransverse ribs. A combination of structuring 21 and structuring 15 ispossible to further improve the fixation effect of the head 9 in thehollow spherical cavity 19.

[0030] The hollow spherical cavity 19 is preferably designed with ashape complementary to that of the head 9 of the pedicle screw 2 to beaccommodated in it.

[0031] The variant shown in FIG. 4 of the device according to thisinvention illustrates the use of a body 3, which is divided into abottom part 52 and a top part 53 across the axis 4 in the middle of thethrough hole 6, in combination with an adjusting nut 26. The bottom part52 of the body 3 must be so tall that the longitudinal bar 1 is alwaysin contact with the bottom part 52.

[0032] The collet chuck 71 differs from the collet chuck 7 shown in FIG.1 only in that the inside thread 11 on the upper end has been replacedby an outside thread 27 for use of an adjusting nut 26. When tightened,the adjusting nut 26 presses on the top part 53 of body 3, whichsubsequently presses directly on longitudinal bar 1. The longitudinalbar 1 is subsequently pressed against the bottom part 52 of the body 3,and then it locks the spherical head 9, as shown in FIG. 2.

[0033] The variant shown in FIG. 5 of the device according to thisinvention differs from the variant illustrated in FIG. 9 only in thatone peg 55 prevents the collet chuck 72, which has been weakened by thechannel 54, from collapsing when the adjusting nut 26 is tightened. Toprevent this peg 55 from falling out, it is advantageously provided withan outside thread and screwed in.

[0034] The variant shown in FIG. 6 of the device according to thisinvention differs from the variant illustrated in FIG. 4 only in that

[0035] a) the collet chuck 73 has an inside thread 11 in addition tooutside thread 27, and

[0036] b) the body 3, which is in one piece, and the through hole 6 arepositioned with respect to the through hole 17 so that only thespherical head 9 is locked when the adjusting nut 26 is tightened. Thispermits distraction or compression with a stable angular position. Theadjusting nut 26 presses on the body 3, and the resulting bracing of thebody 3 with the collet chuck 73 ensures fixation of the spherical head 9of the pedicle screw 2 without locking the longitudinal bar 1. Thelongitudinal bar 1 is pressed separately with the help of the set screw12 against the lower edge of the through hole 6 of the body 3.Therefore, the body 3 is further wedged with the collet chuck 73, whichleads to a greater clamping effect on the spherical head 9. The throughhole 6 must be positioned in the body 3 so that the longitudinal bar 1also rests on the lower edge of the through hole 6 after tightening theadjusting nut 26.

[0037] The variant illustrated in FIG. 7 of the device according to thisinvention differs from the device illustrated in FIGS. 1 through 3 onlyin the design of the locking screw 91 and the positioning of the throughhole 6 with respect to the through hole 17. The collet chuck 7 isprovided with an inside thread 11. A locking screw 91 which is screwedinto the inside thread 11 and a set screw 12 which is integrated intothe locking screw 91 serve to lock the spherical head 9 and thelongitudinal bar 1. The body 3, which is designed in one piece byanalogy with FIGS. 1 through 3, is provided with a turning 94 at thetop, accommodating the shoulder 93 of the locking screw 91. The throughhole 6 is positioned in body 3 with respect to the through hole 17 inthe collet chuck 7 in such a way that only spherical head 9 is lockedwhen locking screw 91 is tightened. The longitudinal bar 1 is securedafterwards by means of the set screw 12. As long as this set screw 12 isscrewed completely into the locking screw 91, and the locking screw 91has been screwed back to the extent that the longitudinal bar 1 touchesthe lower edge of the through hole 6 in the body 3, the spherical head 9can be secured or removed. Furthermore, the collet chuck 7 is releasedagain from the tightened state when the locking screw 91 is screwedback. To accommodate the longitudinal bar 1, the collet chuck 7 may beprovided with a through hole 17 according to FIG. 4, with a channel 54which is open at the top according to FIG. 9, or with a channel 42according to FIG. 8 which is open at the side. In these two cases,either a two-piece design of body 3 or a design according to FIGS. 11and 12 is advantageous to facilitate insertion of the longitudinal bar.However, with the two-piece design, the two parts of the body 3 must bedesigned so that the top part 53 presses directly on the bottom part 52and not on the longitudinal bar 1 even after bracing.

[0038] The variant shown in FIG. 8 of the device according to thisinvention differs from the variant illustrated in FIG. 4 only in that,in contrast with the collet chuck 71, the collet chuck 74 has a channel42 that is open at the side instead of having a through hole 17 toaccommodate the longitudinal bar 1, but the slot 22 does not extend intothis open channel.

[0039] The variant shown in FIG. 9 of the device according to thisinvention differs from the variant illustrated in FIG. 4 only in that,in contrast with the collet chuck 71, the collet chuck 72 has a channel54 that is open at the top instead of a through hole 17 to accommodatethe longitudinal bar 1, and the slot 22 does not extend into this openchannel. To prevent the collet chuck 72 from collapsing when theadjusting nut 26 is tightened, the thread must be designed so thatnegligible radial forces occur in tightening. A sawtooth thread, forexample, would meet this requirement.

[0040] The variant shown in FIG. 10 of the device according to thisinvention illustrates the use of a collet chuck 75, which is providedwith an inside thread 11 instead of an outside thread 27, in contrastwith the collet chuck 72 illustrated in FIGS. 5 and 9. A set screw 56with an outside thread 57 and a flange 58 serves as the clamping means.When tightened, the set screw 56 presses against the longitudinal bar 1,which presses in turn on the bottom part 52 of the body 3. This bracingof the bottom part 52 and the collet chuck 75 locks the spherical head 9of the pedicle screw 2, as illustrated in FIG. 2. The top part 53 of thebody 3 prevents widening of the collet chuck 75 when the set screw 56 istightened. The top part 53 rests on the shoulder 63.

[0041] The variant shown in FIG. 11 of the device according to thisinvention differs from the variant illustrated in FIG. 6 only in thatthe collet chuck 76, in contrast with the collet chuck 73, has a channel42 that is open at the side instead of a through hole 17, and the slots22 do not extend into the channel.

[0042] According to FIG. 13, the through hole 6 in the body 3 ispreferably open at the side (80) to permit unhindered insertion oflongitudinal bar 1.

[0043] The variant shown in FIG. 12 of the device according to thisinvention differs from the variant illustrated in FIG. 11 only in that,in contrast with the collet chuck 76, the collet chuck 77 has a channel54 that is open at the top to accommodate the longitudinal bar 1.According to FIG. 14, the through hole 6 in the body 3 is open towardthe top (81) for unhindered insertion of the longitudinal bar 1.

[0044] The variant shown in FIG. 13 of the device according to thisinvention differs from the variant illustrated in FIG. 11 only in that athrough hole 80 which is open at the side is provided in the body 3.

[0045] The variant shown in FIG. 14 of the device according to thisinvention differs from the variant illustrated in FIG. 12 only in that athrough hole 81 which is open at the top is provided in the body 3.

What is claimed is:
 1. A spinal fixation system comprising: alongitudinal member positionable along a spinal column; a fastenerhaving a head and a threaded end for engaging a vertebra; and aconnector for connecting the fastener and the longitudinal membercomprising: a body having top, bottom, and side surfaces which surroundan interior of the body, with the side surface having a through hole forreceiving the longitudinal member and the bottom surface having anopening leading to the interior of the body; a collet chuck configuredand dimensioned to be slideably received in the interior of the body andhaving a through hole alignable with the body through hole for insertionof the longitudinal member in the connector, a plurality of resilienttongues, and a chamber defined by inner surfaces of the tongues andconfigured and dimensioned to receive the fastener head, the tonguesflexing outward for receiving the fastener head in the chamber andflexing back inward for retaining the fastener head in the chamber; anda locking element for securing the longitudinal member in the body andcollet chuck through holes, wherein engagement of the locking elementresults in inward movement of the tongue and thereby secures thefastener at a surgeon selected angle.